Translatable scanner calibration target

ABSTRACT

In one example, a document scanner has a fixed-position scan bar and a built-in translatable calibration target. The scan bar has a linear array of imaging elements aimed in an imaging direction. The calibration target is spaced apart from and parallel to the linear array, and has a planar surface orthogonal to the imaging direction spanning the length of the linear array. The target is translatable during a calibration in a direction in a plane of the surface.

BACKGROUND

Optical image scanners are widely used for generating digitalrepresentations of real-world objects, particularly media such asdocuments which may include text, graphics, printed images, and thelike. With flatbed scanners, media is maintained in a fixed position ona platen during scanning by a moveable scan bar. Alternatively, withdocument scanners (also called sheet-fed scanners), the media is fedpast a fixed-position scan bar during scanning. In order to generatedigital representations having high image quality, calibration of thescanner may be desirable. For some scan bar technologies, re-running thecalibration may be desirable in order to ensure high image quality overtime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a document scanner having afixed-position scan bar and a built-in translatable calibration targetin accordance with an example of the present disclosure.

FIG. 2 is a schematic representation of the document scanner having afixed-position scan bar and a built-in translatable calibration targetwith a document fed therethrough for scanning in accordance with anexample of the present disclosure.

FIG. 3 is an exploded isometric representation of a bias plate assemblyhaving a translatable calibration target, and drive system for theassembly of a document scanner in accordance with an example of thepresent disclosure.

FIG. 4 is an assembled isometric representation of the bias plateassembly of FIG. 3 in accordance with an example of the presentdisclosure.

FIG. 5A is an isometric representation of a carrier and a base of thebias plate assembly of FIGS. 3-4 in accordance with an example of thepresent disclosure.

FIG. 5B is a two-dimensional top view of a base of the bias plateassembly of FIGS. 3-4 for translating the calibration target in adirection orthogonal to an array of imaging elements of a scan bar, inaccordance with an example of the present disclosure.

FIG. 5C is a two-dimensional top view of a base of the bias plateassembly of FIGS. 3-4 for translating the calibration target in adirection non-orthogonal to an array of imaging elements of a scan bar,in accordance with an example of the present disclosure.

FIG. 6A is a schematic side view of the scanner showing the bias plateassembly of FIG. 3 in a rear-most document scanning position, inaccordance with an example of the present disclosure.

FIG. 6B is a schematic side view of the scanner showing the bias plateassembly of FIG. 3 in a front-most position following translation duringcalibration, in accordance with an example of the present disclosure.

FIG. 7 is an isometric representation of an array of multiple offset,staggered bias plate assemblies each having a translatable calibrationtarget, and a common drive system for the assemblies, of a documentscanner in accordance with an example of the present disclosure.

FIG. 8 is a schematic side representation of a document scanner havingan array of scan bars positioned in an operational position and in aservice position, in accordance with an example of the presentdisclosure.

FIG. 9 is a flowchart in accordance with an example of the presentdisclosure of a method of calibrating a document scanner without use ofa calibration document.

FIG. 10 is a flowchart in accordance with an example of the presentdisclosure of a method of scanning a document with the document scannerof FIG. 9.

DETAILED DESCRIPTION

Scan bars may utilize different technologies for their imaging elements.One type of scan bar may use CCD (charge-coupled device) elements.Another type of scan bar may use CIS (contact image sensor) elements.Each type may have its own characteristics. A CIS scan bar, for example,is relatively low in cost, small in size, high in resolution, and low inpower usage. However, CIS lens arrays have a shallow depth of field.Objects positioned within 0.2 mm of the glass of the CIS module yieldthe best image quality when scanned. Scan quality degrades withincreased distance to the CIS module lens array. CIS scan bars alsoprovide the best image quality when they are periodically recalibrated.

As defined herein and in the appended claims, a “document scanner” maybe broadly understood to be an optical imaging device in which documentsto be scanned flow or are fed past a fixed-position scan bar of thescanner during an image scanning operation. As defined herein and in theappended claims, a “fixed-position scan bar” is a scan bar which doesnot move during a scanning operation performed by the document scanner.

One approach to calibrating scan bars in document scanners involves auser feeding and scanning a special calibration document. However, dueto the user interaction, such a calibration cannot be performedautomatically. Image quality of scan output can be degraded if the userdelays or omits this manual calibration. And the special calibrationdocuments can be easily damaged, and may be expensive and inconvenientto replace. Thus this approach to calibration often gives a poor userexperience.

Another approach to calibrating scan bars in document scanners uses acylindrical rotating calibration target built into the scanner. Whilethis avoids the need for a special calibration document, the cylindermay have run-out or other characteristics such that the axis of rotationis not aligned with the lens array, or the cylinder is not flat againstthe scan bar. In the case of a CIS scan bar, due to the shallow depth offield, a scan of the calibration target using a cylinder which has suchmisalignment can result in a significant luminance change across thescanned image which degrades image quality. A similar luminance changecan also occur where the cylindrical rotating calibration target alsoserves as a background when scanning transparent or translucentdocuments.

Yet another approach to calibrating fixed-position scan bars in documentscanners uses a flat, static calibration target built into the scanner.A flat target helps to avoid luminance changes across the scan bar.However, if the target gets damaged (e.g. scratched, blemished, orcovered with dust or contaminants), the calibrations may be unsuccessfulor inaccurate as a result of some of the imaging elements imaging thedamaged portions of the target surface, resulting in poor image qualityfrom scans using the calibration results. In addition, it may bedifficult and expensive to replace the target in the scanner, and thistype of service operation usually cannot be done by a user.

Referring now to the drawings, there is illustrated an example of adocument scanner with a built-in calibration target which canautomatically perform calibrations without the use of a specialcalibration document and which can perform successful calibrations evenwith some imperfections in or on the calibration target. The documentscanner includes a fixed-position scan bar having a linear array ofimaging elements aimed in an imaging direction orthogonal to the array.Spaced apart from, and parallel to, the linear array is a translatablecalibration target that has a planar surface orthogonal to the imagingdirection which spans the length of the linear imaging element array.The target is translatable, during a calibration, in a direction in aplane of the surface.

Considering now one example document scanner, and with further referenceto FIG. 1, a scanner 100 has a scan bar 110. The scan bar 110 isattached to a portion 105 of the scanner 100 in a fixed position, andthe scan bar 110 does not move during a scan or imaging operation. Thescan bar 110 has a substantially linear array of imaging elements 112(several of which are illustrated). The imaging elements 112 each has afield of view, and are aimed in an imaging direction 114 orthogonal tothe linear array. The scan bar 110 may include a lens array (not shown)that causes the field of view to have a predefined depth of field. Insome examples, the lens array is a rod lens array.

The scanner 100 also has a built-in, translatable calibration target140. The target 140 is spaced apart from, and parallel to, the scan bar110. More particularly, the target 140 has a planar, flat surface 142which is orthogonal to the imaging direction 114. The planar surface 142defines an X-Y plane of a coordinate system 102. The target 140 has asize in the X direction that spans at least the distance in the Xdirection viewed by the scan bar 110, and a size in the Y direction thatspans at least the distance in the Y direction viewed by the scan bar110 throughout the translation of the target 140. The planar surface 142is spaced apart from a planar surface 116 of the scan bar 110 by adistance S 120 in the Z direction of the coordinate system 102. In someexamples, the spacing S 120 may be less than a predefined distance. Insome examples the imaging elements 112 may be CIS elements, and thespacing S 120 may be 0.2 millimeters or less. Each imaging element 112may view a corresponding imaged region 144 of the planar surface 142 fora given position of the target 140.

The target 140 is translatable within the scanner 100, and thustranslatable with respect to the fixed-position scan bar 110. The target140 translates in a given direction in the X-Y plane so as to maintainthe spacing S 120 during translation. Thus the target 140 is wider inthe Y direction than the size of an imaged region 144. In one example,the target 140 may translate by a distance of at least 0.20 millimeters.In another example, the target 140 may translate by a distanceproportional to the size of the defect and the size of the imaged region144, such that scan output corresponding to the defect can be excluded.In some examples, the target 140 translates during a calibrationoperation, and is maintained in a fixed position during a documentscanning operation. The fixed position used during document scanning maybe predefined.

The direction of translation of the target 140 in the X-Y plane, in someexamples, may be in a direction 146 that is orthogonal to the lineararray of imaging elements 112. In this case, the imaged region 144 movesalong a linear zone 147 of the planar surface 142. In other examples,the direction of translation of the target 140 in the X-Y plane is in adirection 148 that is non-orthogonal to the linear array of imagingelements 112. In that case, the imaged region 144 falls along a linearzone 149 of the planar surface 142. As discussed subsequently in greaterdetail, the non-orthogonal direction 148 may provide increasedcalibration robustness in case of a blemished or damaged target surface142. The target 140 has a sufficient width in the Y direction to ensurethat all of zones 147, 149 fall onto the target 140.

In some examples, the planar surface 142 of a target 140 (which is notdamaged or blemished) is substantially uniform in color. In someexamples, this planar surface 142 is substantially white in color.

Considering now an example document scanner performing a documentscanning operation, and with reference to FIG. 2, a document scanner 200includes the scan bar 110 and the target 140. A document 220 is fedthrough the scanner 200 between the scan bar 110 and the target 140 in apredetermined direction 205. The target 140 is attached to, or in somecases integral to, a bias plate assembly 250. The bias plate assembly250 maintains the surface 222 of the document 220 at a spacing from thesurface 116 of the scan bar 110 which allow high quality imaging. Insome examples, the bias plate assembly 250 does this by contacting thedocument 220 and urging the opposite surface 222 of the document 220against the surface 116 of the scan bar 110. To accommodate variousthicknesses of the document 220, at least an upper portion of the biasplate assembly 250, which may include the target 140, is movable in theZ direction of the coordinate system 102 so as to allow the surface 222of various documents to be properly spaced apart from the surface 116.The upper portion of the bias plate assembly 250, including the target140, may also be compliant so as to conform to irregularities in thesurface 116 of the scan bar 110 and/or the document 220, particularly insituations where the bias plate assembly 250 contacts the surface 116directly, or indirectly via the document 220.

In some examples, the direction of translation in the X-Y plane of thetarget 140 is the same as the document feed direction 205. In otherexamples, the direction of translation of the target 140 is a differentdirection in the X-Y plane from the document feed direction 205.

In some examples, the calibration target 140 also provides a backgroundfor a transparent or translucent document 220 during scanning. Whenscanning such documents, scan defects including shadows can result ifthe scanner 100, 200 does not provide a background of a uniform color(in some examples, white) for the portion of the document being scanned.The uniform color of the target 140 minimizes or prevents such scandefects when scanning generally transparent or translucent documents220.

Considering now one example of a bias plate assembly having atranslatable calibration target, and with reference to FIGS. 3 and 4, abias plate assembly 300 includes a base 310, a carrier 320, at least oneresilient member (which can take many forms as described below), and abias plate 340 having a calibration target 350. The bias plate assembly300 is coupled to a drive system 370 that is coupled to the carrier 320to controllably slide the carrier 320 relative to the base 310. Thedrive system includes a drive 375, a cam shaft 380, at least one cam385, and a bearing 390. FIG. 3 depicts an exploded view of the biasplate assembly. FIG. 4 depicts an assembled view of the bias plateassembly. In some examples, the bias plate assembly 300 is constructedmostly of low-cost molded plastic parts.

The bias plate 340 has the calibration target 350 attached to it, orintegrally formed in or on it. The calibration target 350 is flat anduniform in color, and may be the calibration target 140 (FIGS. 1-2). Alow rib 342 extends above the target 350 in the Z direction of thecoordinate system 302. When the bias plate 340 is in contact with adocument 220 (FIG. 2) being scanned, or with the surface 116 of the scanbar 110 (FIGS. 1-2), the rib 342 creates a small gap between the surface116 and the target 350. This gap maintains a predefined spacing betweenthe surface 116 and the target 350, and also protects the target 350from wear due to contact with the document 220 or with the surface 116of the scan bar 110. The bias plate 340 is flexible and compliant so asto conform to the surface 116. In one example, the bias plate 340 ismolded of a low-cost uniform white ABS (acrylonitrile butadiene styrene)plastic material. In other examples, the bias plate 340 may be metal oranother substance. The bias plate 340 also has a ramped lead-in surface344 to assist with smoothly feeding the document 220 between the scanbar 110 and bias plate 340 and preventing jamming. At least one snap 346of the bias plate 340 fixedly attach the bias plate 340 to the carrier320. The snaps 346 allow the bias plate 340, including the target 350,to be snapped off the carrier 320 to allow convenient replacement by auser instead of specially trained service personnel.

The resilient members collectively provide sufficient preload of thebias plate 340 to urge the bias plate 340 toward the surface 116 of thescan bar 110. In one example, each resilient member is a coil spring330. In other examples, the resilient member is a leaf spring, acompressible material, or another suitable component. If no document isinserted for scanning, the coil springs 330 urge the bias plate 340against the surface 116 of the scan bar 110. If a document is insertedfor scanning, the coil springs 330 urge the bias plate 340 against thedocument 220 whose surface 222 is in turn urged against the surface 116of the scan bar 110. The coil springs 330 are tuned with regard to theforce they apply in order to minimize or eliminate document jamming.

The carrier 320 retains the bias plate 340 and houses the coil springs330. Each end of a coil spring 330 may be engaged by a post 322 on thecarrier, and a corresponding post (not shown) on the bias plate 340.Each snap 346 connects to a corresponding receptacle 324. Force appliedby the coil springs 330 to the bias plate 340 and carrier 320 assist inmaintaining the connection between the bias plate 340 and the carrier320. Disposing coil springs 330 at various intervals along the length ofthe carrier 320 allows each to be compressed a different amount, whichassists the bias plate 340 to conform to irregularities in the surface116 of the scan bar 110 and/or the document 220 to maintain the properspacing to the scan bar 110.

The carrier 320 includes at least one pair of cam engagement pockets326A, 326B (collectively 326). The pockets 326 may have an upside-down Ushape sized to engage cams of the drive system 370, as discussed in moredetail subsequently with reference to FIGS. 6A-6B, in order to translatethe bias plate 340. Pockets 326A extend along the Y axis from a frontside of the carrier 320, while pockets 326B extend along the Y axis fromthe opposite rear side of the carrier 320. Pockets 326A, 326B facilitatethe use of multiple bias plate assemblies with a single drive system, asdiscussed subsequently with reference to FIG. 7.

The carrier 320 also includes at least one base engagement feature onthe underside of the carrier 320. The base engagement feature may be, inone example, a rib 328 which slideably engages a guide feature on thebase 310 to facilitate translation of the bias plate 340. In otherexamples, the base engagement feature is a pin, a slot, or anothersuitable feature.

The base 310 retains the carrier 320. In one example, at least one hook312 on the base 310 each engage a corresponding slot 329 on the carrier320. The base 310 also attaches the carrier 320 to the chassis (notshown) of the scanner. The base 310 is attached to the chassis in afixed position. The base 310 also translatably engages the carrier 320.In some examples, the base 310 and carrier 320 are slidably engaged.This engagement is via at least one guide feature on the base 310. Inone example, the guide feature is a guide slot 314 which engages amating rib 328 of the carrier 320. The guide slot 314 controls thedirection of translation of the bias plate 340, as discussedsubsequently with reference to FIGS. 5A-5C.

Regarding the drive system 370, the drive 375 controllably rotates thecam shaft 380 to which it is coupled by a desired amount. For simplicityof illustration, the drive 375 is depicted as a single gear fixed to thecam shaft 380, and other portions of the drive 375 are not shown.

The cam shaft 380 rotates under control of the drive 375. At least onecam 385 is disposed at an angular position on the cam shaft 380. Theshape and position of the cams 385 control the speed and distance of thebias plate translation as the cam shaft 380 is rotated. The cams 385that engage an individual bias plate assembly are usually disposed atthe same angular position on the cam shaft 380.

Each bearing 390 supports and locates the cam shaft 380. Each bearing390 is affixed to the chassis of the scanner. In one example, thebearing is formed of a lubricious material with a favorable tribologysuch that the cam shaft 380 can rotate without excessive drag over thelifetime of the scanner.

In other examples, alternative mechanisms for translating the bias plate340 may be utilized. As one example, a rack-and-pinion system coulddispose a small gear mesh on the bottom of the carrier 320 to engagewith a corresponding gear on the cam shaft 380.

Considering now in greater detail the carrier 320 and the base 310, andwith reference to FIGS. 5A-C, the direction of translation of the biasplate 340 is governed by the direction of the rib 328 and the guide slot314. In one example, the base 310A of FIG. 5B provides for translatingthe bias plate 340 (and the calibration target 350) in a direction 502Athat is orthogonal to the linear array of imaging elements 112 of thescan bar 110 (FIGS. 1-2). In this case, the guide slot 314A and the rib328 extend in the orthogonal direction 502A.

In another example, the base 310B of FIG. 5C provides for translatingthe bias plate 340 (and the calibration target 350) in a direction thatis non-orthogonal to the linear array of imaging elements 112 of thescan bar 110. In this case, the guide slot 314B and the rib 328 extendin the non-orthogonal direction 502B. Such non-orthogonal translationmay be advantageous in distinguishing a defective imaging element 112from a scratch or blemish on the calibration target 350 that is orientedin the direction of translation and long enough to span the entiredistance of translation. This is because, if the direction oftranslation is orthogonal to the linear array of imaging elements 112 ofthe scan bar 110, the entire scratch or blemish on the calibrationtarget 350 that is oriented in the direction of translation is capturedby the same imaging element(s) 112 throughout the translation. However,if the direction of translation is non-orthogonal to the linear array ofimaging elements 112 of the scan bar 110, any scratch or blemish on thecalibration target 350 will be captured by different imaging elements112 as the target 350 is translated. This indicates that these variousimaging elements 112 themselves are all functional, and that thecalibration target 350 is scratched or blemished. As discussedsubsequently with reference to FIG. 9, a scratch or blemish can becompensated for when doing the calibration.

In some examples, the length of each slot 329 on the carrier 320 islonger in the direction of translation of the bias plate 340 than thelength of its corresponding hook 312 on the base 310. This allows theslot 329 to translate with respect to the hook 312 during translation ofthe bias plate 340. The hook 312, and its mating slot 329, are angled inthe same direction 502A, 502B as the guide slot 314 and rib 328. Hooks312A, 312B of FIGS. 5B-5C illustrate such angling for the orthogonal andnon-orthogonal case respectively.

Considering now the translation of the bias plate 340 including thecalibration target 350, and with reference to a schematic side views ofFIGS. 6A-6B of certain portions of the scanner, the scanner is orientedsuch that the front is to the left and the rear to the right. The base310 is fixed to the scanner chassis 630. The calibration target 350, anda portion of the bias plate 340, protrude above a document-receivingplaten 620 through an aperture in the platen 620. In FIG. 6A, the biasplate 340 and calibration target 350 are positioned at a rear-mostdocument scanning position, and the coil springs 330 have urged the rib342 of the bias plate into contact with the viewing surface 612 of ascan bar 610. The cam shaft 380 is rotated clockwise an amount such thatthe cam 385 contacts the external right side wall of the pocket 326B ofthe carrier 320, and continues to rotate to translate the carrier 320and its attached bias plate 340 and calibration target 350 into therear-most document scanning position, where it is maintained duringscanning. A document is fed into the scanner in direction 604 above theplaten 620, and the lead-in 344 of the bias plate 340 directs thedocument between the rib 342 and the viewing surface 612. The bias plate340 is pressed down by the document to allow it to flow through thescanner, compressing the coil spring 330 a corresponding amount. Thedocument is imaged by the scan bar 610 at the line-of-sight 614. The rib342 serves as the wear point for contact with the document and creates agap 616 between the calibration target 350 and the scan bar viewingsurface 612, thus protecting the calibration target 350 from damage bythe document.

In FIG. 6B, the bias plate 340 and calibration target 350 areillustrated positioned at a front-most position within the scanner,after being translated a distance in a direction having at least acomponent 618 in the −Y direction of the coordinate system 602 during acalibration process. In the calibration process, no document is insertedin the scanner. To translate the bias plate 340 and calibration target350, the cam shaft 380 is rotated counter-clockwise an amount such thatthe cam 385 contacts the internal left side wall of the pocket 326B ofthe carrier 320, and continues to rotate to translate the carrier 320and its attached bias plate 340 and calibration target 350 from therear-most position into the front-most position. During translation, theimaging elements of the scan bar 610 each image a zone (e.g. zone 147 orzone 149, FIG. 1) of the calibration target 350. In the front-mostposition of FIG. 6B, the line-of-sight 614 views a different position ofthe calibration target 350 than the rear-most position of FIG. 6A. Thecalibration process is described subsequently in greater detail withreference to FIG. 9.

Considering now an example array of multiple offset, staggered biasplate assemblies for a corresponding array of multiple offset,staggered, fixed-position scan bars, and with reference to FIG. 7, amultiple scan bar array may be used for scanning documents having widthsgreater than the span of a single scan bar. The scan bars may be offsetfrom each other so as to provide an overlap area between every two scanbars where both scan bars can image the corresponding portion of thedocument. The images captured by each scan bar can be stitched togetherto form a composite image representing the entire document.

An example array 700 includes three translatable bias plate assemblies710A-710C (collectively 710). Each bias plate assembly 710 may be thebias plate assembly 300 (FIG. 4), and each bias plate assembly 710includes a calibration target. In FIG. 7, a portion of each end biasplate assembly 710A, 710C is illustrated, while all of the middle biasplate assembly 710B is illustrated. Each bias plate assembly 710includes a calibration target 350.

The example array 700 has a single common drive system that translatesall of the bias plate assemblies 710 and calibration targets. The cams385 on the single cam shaft 380 may engage the front pockets 326A or therear pockets 326B of an individual bias plate assembly 710. For example,the cams 385 engage the rear-side pockets 326B of each end bias plateassembly 710A, 710C, while the cams 385 engage the front-side pockets326A of the middle bias plate assembly 710A.

In scanners with a multiple bias plate assembly array 700, the biasplate assemblies 710 may translate in the same direction. In someexamples, the cams 385 are fixed at the same angular position on the camshaft 380 so as to translate all bias plate assemblies 710 synchronouslyor in unison. In other examples, the cams 385 for each bias plateassembly 710 can be fixed at different angular positions on the camshaft 380 so as to translate the various bias plate assemblies 710sequentially. Sequential translation of bias plate assemblies may beuseful in reducing bandwidth requirements for calibration processing,since the calibration of different scan bars can be performed atdifferent times, rather than simultaneously.

Considering now a schematic representation of an example documentscanner, and with reference to FIG. 8, a scanner 800 includes pluralscan bars 810 in a staggered arrangement. A platen 820 is located on thesurface of a housing 805, a portion of which is illustrated. The upperportion of bias plate assemblies 830 each having a calibration targetprotrudes from the housing 805 above the platen 820. Each bias plateassembly 830 may be the bias plate assembly 300 (FIG. 4). The scanner800 also includes a document transport mechanism 840, a drive system 850for the bias plate assemblies 830, and a controller 860. The controller860 is communicatively coupled to the document transport mechanism 840,the drive system 850, and the scan bars 810.

The controller 860 includes a processor 862 coupled to acomputer-readable medium such as a memory 864. The processor 862executes instructions 866 stored in the memory 864 to control thedocument transport mechanism 840 to feed documents through the scanner800, the scan bars 810 to image the documents and/or the calibrationtargets, and drive system 850 to translate the bias plates andcalibration targets of the bias plate assemblies 830.

The scan bars 810 may be attached to a structural member of the scanner800. In some examples, the structural member is attached to a movablecover of the scanner 800. The structural member is depicted in twodifferent positions: an operating position 870 (solid line) and aservice position 870′ (dashed line).

During operation, the structural member positions scan bars 810 in theirnormal operating position 870 adjacent bias plate assemblies 830. Forservicing the bias plate assemblies 830 or other purposes, the scan bars810 are moved out of their operational position when the structuralmember is moved to the service position 870′. In the service position870′, the user of the scanner has access to the bias plate assemblies830, and can easily clean, remove, and/or replace the bias plate (e.g.bias plate 340, FIGS. 3-4).

Consider now, with reference to FIG. 9, one example method forcalibrating a document scanner without use of a calibration document fedthrough the scanner. The flowchart of FIG. 9 may be considered as stepsin a method implemented in the scanner, or in its controller.Alternatively, the flowchart of FIG. 9 may be considered as a flowchartof at least a portion of the scanner or its controller. The scanner maybe the scanner 100 (FIG. 1), 200 (FIG. 2), or 800 (FIG. 8). A method 900begins at 902 by controllably moving a planar, flat translatablecalibration target built into the scanner a predetermined distancerelative to a fixed-position scan bar of the scanner. The target may bemoved from an initial position used during document scanning. In someexamples, the calibration target is translated within the plane of thesurface of the calibration target. In some examples, at 904, thecalibration target is moved in a direction different from a documentfeed direction of the document through the scanner.

At 906, the calibration target is repeatedly imaged with the scan barduring the moving such that each imaging element of the scan barcaptures image signals for a zone (e.g. zone 147 and/or 149) of a flatsurface of the calibration target. In some examples, at 910, thecalibration target is urged against an imaging surface of the scan barduring the moving.

At 912, the captured image signals from each imaging element areprocessed to calibrate the scanner. In some examples, at 914, where thecalibration target 140 (FIGS. 1-2), or its planar surface 142, is auniform white color, the processing includes calibrating the scan barfor white point and uniformity. Each imaging element of a scan bar mayhave a different response characteristic (photo response non-uniformity,or PRNU) from other imaging elements. Calibrating for white pointinvolves generating a white point calibration constant per color for animaging element based on the output of that imaging element resultingfrom scanning the white calibration target. Calibrating for uniformityinvolves generating these calibration constants for all imaging elementsof the scan bar in order to make the response from all imaging elementsuniform across the scan bar. Doing so can also account fornon-uniformities in the light source of the scanner which illuminatesthe object (in this case the calibration target) which is being scanned.These calibration constants are then utilized during subsequent scans togenerate a uniform response having the correct color balance from allthe imaging elements of the scan bar. In determining white point anduniformity, the series of images corresponding to the zone (e.g. zone147 and/or 149) imaged by an imaging element during translation of thecalibration target are processed. Such processing 912 reduces oreliminates the effect on the white point and uniformity of blemishes,scratches, or other damage to the calibration target. For example, theprocessing may average the series of images, or may discard or give lessweight to outliers in the series of images which may correspond to thedamage. As a result, the processing 912 generates a more accuratecalibration than a calibration which is based on measurements made witha static calibration target.

Consider now, with reference to FIG. 10, one example method for scanninga document. The flowchart of FIG. 10 may be considered as steps in amethod implemented in the scanner, or in its controller. Alternatively,the flowchart of FIG. 10 may be considered as a flowchart of at least aportion of the scanner or its controller. The scanner may be the scanner100 (FIG. 1) or 800 (FIG. 8). A method 1000 begins at 900 by calibratinga document scanner without use of a calibration document being fedthrough the scanner. In some examples, at 1002, the calibration 900 isautomatically initiated by the scanner without user intervention andwithout feeding a calibration medium into the scanner. In some examples,at 1004, a user replaces the calibration target prior to the calibration900. In some examples, at 1006, the calibration target is returned to aninitial position after the calibration 900. The initial position may bea document scanning position of the target.

At 1008, a document is fed through the scanner between the scan bar andthe calibration target. At 1010, strips of the document are sequentiallyimaged with the scan bar as the document is being fed through thescanner. During this imaging, the calibration target is maintained inthe initial (scanning) position. At 1012, the imaged strips areprocessed to construct a digital representation of the scanned document.

Terms of orientation and relative position (such as “top,” “bottom,”“side,” and the like) are not intended to require a particularorientation of any element or assembly, and are used for convenience ofillustration and description.

In some examples, at least one block or step discussed herein isautomated. In other words, apparatus, systems, and methods occurautomatically. As defined herein and in the appended claims, the terms“automated” or “automatically” (and like variations thereof) shall bebroadly understood to mean controlled operation of an apparatus, system,and/or process using computers and/or mechanical/electrical deviceswithout the necessity of human intervention, observation, effort and/ordecision.

From the foregoing it will be appreciated that the document scanner andmethods provided by the present disclosure represent a significantadvance in the art. To recap just a few aspects of this advance, a largeplanar calibration target parallel to the scan bar minimizes sensitivityto part and assembly tolerances, and minimized luminance variationduring calibration and scanning. A relatively long distance oftranslation of the calibration target during a calibration processmaximizes the ability to compensate for damage to, or blemishes on, thecalibration targets. And where the translation of the calibration targetduring calibration is non-orthogonal to the linear array of the scanbar, damage or blemishes on the target can be distinguished fromdefective imaging elements and can be factored out of the calibration.Where the spacing between the calibration target and a translucent ortransparent document scanned is sufficiently small, the calibrationtarget provides a shadow-eliminating background during scanning. Aleading rib protects the calibration target from damage during documentscanning, and the calibration target can be easily cleaned or replacedby the user of the scanner.

Although several specific examples have been described and illustrated,the disclosure is not limited to the specific methods, forms, orarrangements of parts so described and illustrated. This descriptionshould be understood to include all novel and non-obvious combinationsof elements described herein, and claims may be presented in this or alater application to any novel and non-obvious combination of theseelements. The foregoing examples are illustrative, and no single featureor element is essential to all possible combinations that may be claimedin this or a later application. Unless otherwise specified, steps of amethod claim need not be performed in the order specified. Similarly,blocks in diagrams or numbers (such as (1), (2), etc.) should not beconstrued as steps that must proceed in a particular order. Additionalblocks/steps may be added, some blocks/steps removed, or the order ofthe blocks/steps altered and still be within the scope of the disclosedexamples. Further, methods or steps discussed within different figurescan be added to or exchanged with methods or steps in other figures.Further yet, specific numerical data values (such as specificquantities, numbers, categories, etc.) or other specific informationshould be interpreted as illustrative for discussing the examples. Suchspecific information is not provided to limit examples. The disclosureis not limited to the above-described implementations, but instead isdefined by the appended claims in light of their full scope ofequivalents. Where the claims recite “a” or “a first” element of theequivalent thereof, such claims should be understood to includeincorporation of one or more such elements, neither requiring norexcluding two or more such elements. Where the claims recite “having”,the term should be understood to mean “comprising”.

What is claimed is:
 1. A document scanner, comprising: a fixed-positionscan bar having a linear array of imaging elements aimed in an imagingdirection; and a built-in translatable calibration target spaced apartfrom and parallel to the linear array, the target having a planarsurface orthogonal to the imaging direction and spanning the length ofthe linear array, and the target translatable during a calibration in adirection in a plane of the surface.
 2. The scanner of claim 1,comprising: a compliant bias plate having the calibration target; and aresilient member to urge the compliant bias plate toward the lineararray.
 3. The scanner of claim 2, comprising: a carrier removablyattached to the compliant bias plate; a base translateably attached tothe carrier and fixedly attached to a chassis of the scanner; andwherein the resilient member is retained between the bias plate and thecarrier, the bias plate movable toward the carrier in the imagingdirection to compress the resilient member.
 4. The scanner of claim 3,comprising: a drive system coupled to the carrier to controllablytranslate the carrier relative to the base.
 5. The scanner of claim 2,wherein the resilient member is to urge the bias plate against a housingof the linear array, and wherein the bias plate conforms to a contactingsurface of the housing.
 6. The scanner of claim 5 wherein a rib of thecompliant bias plate is urged against the housing, the rib maintaining apredefined spacing between the calibration target and the housing. 7.The scanner of claim 1, wherein the planar surface of the calibrationtarget has a uniform color and is a background for scanning transparentand translucent documents.
 8. The scanner of claim 1, wherein thedirection of target translation in the plane of the planar surface isnon-orthogonal to the linear array of imaging elements.
 9. A method ofcalibrating a document scanner without a calibration document,comprising: controllably moving a flat translatable calibration targetbuilt into the scanner a predetermined distance relative to afixed-position scan bar of the scanner; during the moving, repeatedlyimaging the calibration target with the fixed-position scan bar suchthat each imaging element of the fixed-position scan bar capturessignals for a zone of a flat uniform color surface of the calibrationtarget; and processing the captured signals from each imaging element tocalibrate the scanner.
 10. The method of claim 9, wherein the processingincludes calibrating at least one of white point and uniformity of thefixed-position scan bar.
 11. The method of claim 9, wherein the movingmoves the calibration target in a direction different from a documentfeed direction.
 12. The method of claim 9, further comprising, after theprocessing: returning the calibration target to an initial position;feeding a document through the scanner between the fixed-position scanbar and the calibration target; during the feeding, sequentially imagingstrips of the document with the fixed-position scan bar with thecalibration target in the initial position; and processing the imagedstrips to construct a digital representation of the document.
 13. Themethod of claim 9, further comprising: during the moving, urging thecalibration target against a surface of the fixed-position scan bar. 14.A document scanner, comprising: a scan bar array of overlappingstaggered fixed-position scan bars each having a linear array of imagingelements; an array of overlapping staggered translatable calibrationtargets spaced apart from and parallel to the scan bar array, eachtarget having a planar surface that spans a length of a correspondingimaging element array and is imageable by the imaging elements of thecorresponding linear array; and a single drive system coupled to all thecalibration targets to controllably translate the calibration targetsrelative to the scan bars during a calibration operation.
 15. Thescanner of claim 14, wherein the single drive system comprises: arotatable cam shaft; a plurality of cams each fixed to the cam shaft atan angular position; and a plurality of cam engagement features eachcoupled to a corresponding one of the calibration targets and engagedwith a corresponding one of the cams.